Abstract: The ultrasonic-assisted extracted technique for wax gourd polysaccharide and the antioxidative activity of polysaccharides were studied in this paper. On the basis of single factor experiment, this work studied the effects of solid to liquid ratio, extraction time, and extraction power on the extraction yield of wax gourd polysaccharide. Then the optimal extraction conditions were obtained by the orthogonal experiment. Finally, the in vitro antioxidant ability of wax gourd polysaccharide was characterized by studying its reactivity to DPPH radical，hydroxyl radical，superoxide anion radical. The influences of ultrasonic extraction time and solid to liquid ratio on the extraction rate of wax gourd polysaccharide were significantly（ P < 0. 05）.The suitable ultrasonic-assisted extraction conditions for wax gourd polysaccharide were solid to liquid ratio 1∶40, ultrasonic extraction time 40 min, extraction power 380 W, under the conditions , the yield of crude wax gourd polysaccharide was 13. 15%, compared with the hot water extraction method, the yield increased by more than 50%, the extraction time shorten by 1/2. When the concentration of wax gourd polysaccharides was 5 mg/mL, the clearance rates of DPPH radical, hydroxyl radical and superoxide anion radical were 77. 91%, 99. 64% and 74. 48%, respectively. The ultrasonic- assisted extraction method can significantly improve the extraction efficiency of wax gourd polysaccharide；the wax gourd polysaccharide had good antioxidant activity.

Key words: wax gourd polysaccharides, ultrasonic-assisted extraction, technique optimization, antioxidant activity